In recent years, a pedestrian navigation system using GPS (global positioning system) has been developed. This pedestrian navigation system searches for a route to the destination based on the current position of the pedestrian and map information and displays the found route on a display section (for example, refer to patent document 1). Nowadays, a portable terminal device such as a portable telephone or a PDA installing the navigation system is provided for making it possible to give routing assistance to a pedestrian while conducting telephone conversation or communications.
By the way, a portable telephone provided with a display section such as a liquid crystal display and a key operation section on separate cases so that the terminal cases can be folded with one shaft as the center is provided. In the foldable portable telephone, a microphone and a loudspeaker as magnetism generation sections are provided on separate cases and a magnetism detection section is provided on either of the terminal cases.    Patent document 1: JP-A-2001-204062